Total CH4 Flux Research Articles

Simulated plant-mediated oxygen input has strong impacts on fine-scale porewater biogeochemistry and weak impacts on integrated methane fluxes in coastal wetlands

Methane (CH4) emissions from wetland ecosystems are controlled by redox conditions in the soil, which are currently underrepresented in Earth system models. Plant-mediated radial oxygen loss (ROL) can increase soil O2 availability, affect local redox conditions, and cause heterogeneous distribution of redox-sensitive chemical species at the root scale, which would affect CH4 emissions integrated over larger scales. In this study, we used a subsurface geochemical simulator (PFLOTRAN) to quantify the effects of incorporating either spatially homogeneous ROL or more complex heterogeneous ROL on model predictions of porewater solute concentration depth profiles (dissolved organic carbon, methane, sulfate, sulfide) and column integrated CH4 fluxes for a tidal coastal wetland. From the heterogeneous ROL simulation, we obtained 18% higher column averaged CH4 concentration at the rooting zone but 5% lower total CH4 flux compared to simulations of the homogeneous ROL or without ROL. This difference is because lower CH4 concentrations occurred in the same rhizosphere volume that was directly connected with plant-mediated transport of CH4 from the rooting zone to the atmosphere. Sensitivity analysis indicated that the impacts of heterogeneous ROL on model predictions of porewater oxygen and sulfide concentrations will be more important under conditions of higher ROL fluxes or more heterogeneous root distribution (lower root densities). Despite the small impact on predicted CH4 emissions, the simulated ROL drastically reduced porewater concentrations of sulfide, an effective phytotoxin, indicating that incorporating ROL combined with sulfur cycling into ecosystem models could potentially improve predictions of plant productivity in coastal wetland ecosystems.

Hourly methane and carbon dioxide fluxes from temperate ponds

AbstractPonds are regarded as greenhouse gas (GHG) emission hot spots, but how hot are they? We examined this question by measuring methane (CH4) and carbon dioxide (CO2) fluxes in six forest and open land ponds on grasslands in Denmark during summer and winter. We used floating chambers with do-it-yourself sensors and automated headspace venting, allowing for 7404 hourly measurements. We found highly variable gas fluxes within ponds and between seasons and pond types. Ebullitive CH4 fluxes were more variable than diffusive CH4 fluxes. Ebullition was absent when total CH4 fluxes were lowest (15 µmol m−2 h−1), dominant (> 90%) at the highest fluxes (> 400 µmol m−2 h−1), and increased with water temperature. In summer, a minor daily increase in diffusive fluxes was found on days with high wind speed, while CH4 ebullition remained constant. CO2 fluxes paralleled the day-night balance of photosynthesis and respiration. Mean CH4 ebullition in open and forest ponds exceeded CH4 diffusive fluxes 4.1 and 7.1-fold in summer (avg. 22.5 °C) and 2.3 and 2.5-fold in winter (9.6 °C), respectively. CO2 emissions were higher on a molar basis than CH4 emissions, both in summer and winter, while their annual global warming potentials were similar. Mean annual gas emissions from open and forest ponds (1092 and 2527 g CO2e m−2 y−1) are naturally high due to extensive external input of dissolved CO2 and organic carbon relative to pond area and volume.

European CH4 inversions with ICON-ART coupled to the CarbonTracker Data Assimilation Shell

Abstract. We present the first application of the ICOsahedral Nonhydrostatic model with Aerosols and Reactive Trace gases (ICON-ART) in inverse modeling in inverse modeling of greenhouse gas fluxes with an ensemble Kalman smoother. For this purpose, we extended ICON-ART to efficiently handle gridded emissions, generate an ensemble of perturbed emissions during runtime and use nudging on selected variables to keep the simulations close to analyzed meteorology. We show that the system can optimize total and anthropogenic European CH4 fluxes on a national scale in an idealized setup using pseudo-observations from a realistic network of measurement stations. However, we were unable to constrain the sum of the natural emission sources of comparatively low magnitude. Also regions with low emissions and regions with low observational coverage could not be optimized individually for lack of observational constraints. Furthermore, we investigated the sensitivities towards different inversion parameters and design choices with 15 sensitivity runs using the same idealized setup, demonstrating the robustness of the approach when regarding some minimal requirements of the setup (e.g., number of ensemble members). Subsequently, we applied the system to real in situ observations from 28 European stations for three years, 2008, 2013 and 2018. We used a priori anthropogenic fluxes from the EDGARv6 inventory and a priori natural fluxes from peatlands and mineral soils, inland waters, the ocean, biofuels and biomass burning, and geology. Our results for the year 2018 indicate that anthropogenic emissions may be underestimated in EDGARv6 by ca. 25 % in the Benelux countries and, to a smaller degree, in northwestern France and southern England. In the rest of the domain, anthropogenic fluxes are corrected downwards by the inversion, suggesting an overestimation in the a priori. For most countries, this means that the a posteriori country-total anthropogenic emissions are closer to the values reported to the United Nations Framework Convention on Climate Change (UNFCCC) than the a priori emissions from EDGARv6. Aggregating the a posteriori emissions across the EU27 + UK results in a total of 17.4 Tg yr−1, while the a priori emissions were 19.9 Tg yr−1. Our a posteriori is close to the total reported to the UNFCCC of 17.8 Tg yr−1. Natural emissions are reduced from their a priori magnitude almost everywhere, especially over Italy and Romania–Moldova, where a priori geological emissions are high, and over the United Kingdom and Scandinavia, where emissions from peatlands and wetlands were possibly unusually low during the hot and dry summer of 2018. Our a posteriori anthropogenic emissions for the EU27 + UK fall within the range estimated by global top-down studies but are lower than most other regional inversions. However, many of these studies have used observations from different measurement stations or satellite observations. The spatial pattern of the emission increments in our results, especially the increase in the Benelux countries, also agrees well with other regional inversions.

Assessment of CH4 flux and its influencing drivers in the rice-wheat agroecosystem of the Huai River Basin, China

To understand the CH4 flux variations and their climatic drivers in the rice-wheat agroecosystem in the Huai River Basin of China, the CH4 flux was observed by using open-path eddy covariance at a typical rice-wheat rotation system in Anhui Province from November 2019 to October 2021. The variations and their drivers were then analyzed with the Akaike information criterion method. CH4 flux showed distinct diurnal variations with single peaks during 9:00~13:00 local time. The highest peak was 2.15 µg m-2 s-1 which occurred at 11:00 in the vegetative growth stage in the rice growing season (RGS). CH4 flux also showed significant seasonal variations. The average CH4 flux in the vegetative growth stage in the RGS (193.8±74.2 mg m-2 d-1) was the highest among all growth stages. The annual total CH4 flux in the non-rice growing season (3.2 g m-2, 11.8%) was relatively small compared to that in the RGS (23.9 g m-2, 88.2%). CH4 flux increased significantly with increase in air temperature, soil temperature, and soil water content in both the RGS and the non-RGS, while it decreased significantly with increase in vapor pressure deficit in the RGS. This study provided a comprehensive understanding of the CH4 flux and its drivers in the rice-wheat rotation agroecosystem in the Huai River Basin of China. In addition, our findings will be helpful for the validation and adjustment of the CH4 models in this region.

Impact of Soil Organic Layer Thickness on Soil-to-Atmosphere GHG Fluxes in Grassland in Latvia

Drained organic soils in agricultural land are considered significant contributors to total greenhouse gas (GHG) emissions, although the temporal and spatial variation of GHG emissions is high. Here, we present results of the study on soil-to-atmosphere fluxes of carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4) from drained organic (fen) soils in grassland. A two-year study (from July 2021 to June 2023) was conducted in three research sites in Latvia (Europe’s hemiboreal zone). Soil total respiration (Rtot), CH4 and N2O fluxes were determined using a manual opaque chamber technique in combination with gas chromatography, while soil heterotrophic respiration (Rhet) was measured with a portable spectrometer. Among research sites, the thickness of the soil organic layer ranged from 10 to 70 cm and mean groundwater level ranged from 27 to 99 cm below the soil surface. Drained organic soil in all research sites was a net source of CO2 emissions (mean 3.48 ± 0.33 t CO2-C ha−1 yr−1). No evidence was obtained that the thickness of the soil organic layer (ranging from 10 to 70 cm) and OC stock in soil can be considered one of the main affecting factors of magnitude of net CO2 emissions from drained organic soil. Drained organic soil in grassland was mostly a source of N2O emissions (mean 2.39 ± 0.70 kg N2O-N ha−1 yr−1), while the soil both emitted and consumed atmospheric CH4 depending on the thickness of the soil organic layer (ranging from −3.26 ± 1.33 to 0.96 ± 0.10 kg CH4-C ha−1 yr−1).

Spatial and temporal variability of methane emissions and environmental conditions in a hyper-eutrophic fishpond

Abstract. Estimations of methane (CH4) emissions are often based on point measurements using either flux chambers or a transfer coefficient method, which may lead to strong underestimation of the total CH4 fluxes. In order to demonstrate more precise measurements of the CH4 fluxes from an aquaculture pond, using a higher resolution sampling approach we examined the spatiotemporal variability of CH4 concentrations in the water, related fluxes (diffusive and ebullitive) and relevant environmental conditions (temperature, oxygen, chlorophyll a) during three diurnal campaigns in a hyper-eutrophic fishpond. Our data show remarkable variance spanning several orders of magnitude while diffusive fluxes accounted for only a minor fraction of total CH4 fluxes (4.1 %–18.5 %). Linear mixed-effects models identified water depth as the only significant predictor of CH4 fluxes. Our findings necessitate complex sampling strategies involving temporal and spatial variability for reliable estimates of the role of fishponds in a global methane budget.

Significant methane ebullition from large shallow eutrophic lakes of the semi-arid region of northern China

Eutrophic lakes are a major source of the atmospheric greenhouse gas methane (CH4), and CH4 ebullition emissions from inland lakes have important implications for the carbon cycle. However, the spatio-temporal heterogeneity of CH4 ebullition emission and its influencing factors in shallow eutrophic lakes of arid and semi-arid regions remain unclear. This study aimed to determine the mechanism of CH4 emission via eutrophication in Lake Ulansuhai, a large shallow eutrophic lake in a semi-arid region of China.To this end, monthly field surveys were conducted from May to October 2021, and gas chromatography was applied using the headspace equilibrium technique with an inverted funnel arrangement. The total CH4 fluxes ranged from 0.102 mmol m−2 d−1 to 59.296 mmol m−2 d−1 with an average value of 4.984 ± 1.82 mmol m−2 d−1. CH4 ebullition emissions showed significant temporal and spatial variations. The highest CH4 ebullition emission was observed in July with a grand mean of 9.299 mmol m−2 d−1, and the lowest CH4 ebullition emissions occurred in October with an average of 0.235 mmol m−2 d−1. Among seven sites (S1–S7), the maximum (3.657 mmol m−2 d−1) and minimum (1.297 mmol m−2 d−1). CH4 ebullition emissions were observed at S2 and S7, respectively. As the main route of CH4 emission to the atmosphere in Lake Ulansuhai, the CH4 ebullition flux during May to October accounted for 69% of the total CH4 flux. Statistical analysis showed that CH4 ebullition was positively correlated with temperature (R = 0.391, P < 0.01) and negatively correlated with air pressure (R = 0.286, P < 0.00). Temperature and air pressure were found to strongly regulate the production and oxidation of CH4. Moreover, nutritional status indicators such as TP and NH4+-N significantly affect CH4 ebullition emissions (R = 0.232, P < 0.01; R = −0.241, P < 0.01). This study reveals the influencing factors of CH4 ebullition emission in Lake Ulansuhai, and provides theoretical reference and data support for carbon emission from eutrophic lakes. Nevertheless, research on eutrophic shallow lakes needs to be further strengthened. Future research should incorporate improved flux measurement techniques with process-based models to improve the accuracy from regional to large-scale estimation of CH4 emissions and clarify the carbon budget of aquatic ecosystems. In this manner, the understanding and predictability of CH4 ebullition emission from shallow lakes can be improved.

Methane release from enteric fermentation and manure management of domestic water buffalo in Nepal

Methane (CH4) emission in livestock arises from enteric fermentation (EnF) and manure management (MM). This study develops the country-specific CH4 emission factors (EFs) in both EnF and MM for domestic water buffalo (Bubalus bubalis) and estimates total CH4 emission in Nepal using Intergovernmental Panel on Climate Change (IPCC) Tier 2 methodology. Seasonal field data were collected on morphological characteristics, feed characteristics, and manure management practices of the buffalo. The buffalo population was divided into five age groups, and at least 35 buffalo individuals were measured from each age group in the Hilly and Plain regions of Nepal in the winter and summer seasons. Buffalo adult male (BAM) had the highest body weight of 530 ± 53kg in the plain region and 514 ± 65kg in the Hill region. Similarly, the weight of buffalo calf (BC) was 91 ± 25kg in the plain region and 77 ± 26kg in the Hill region. For different age groups of buffalo, EnF EFs ranged from 34 ± 8 to 90 ± 10kg CH4 head-1year-1 and MM EFs ranged from 2.5 ± 0.5 to 7.5 ± 0.5kg CH4 head-1year-1. The estimated EnF and MM EFs of buffalo were not statistically different by region (p > 0 .05). The total CH4 flux from buffalo was 347.8 Gg year-1 in Nepal, contributing 322.2 Gg year-1 from EnF and 25.6 Gg year-1 from MM. The country-specific EFs are highly recommended for precise computing of the national emissions and carrying out mitigation action.

Three years of biochar and straw application could reduce greenhouse gas and improve rice productivity

ABSTRACT Applying soil amendments such as biochar has been proposed as a means to improve soil properties and reduce greenhouse gas emission from agricultural soils. The objective of this study was to evaluate and compare the effects of biochar and straw application on rice yield, select soil properties, global warming potential (GWP), and greenhouse gas intensity (GHGI) over the 3-year period. The study treatments included control (CN), barley straw biochar (BC, 2,000 kg ha−1), barley straw (BS, 2,000 kg ha−1), and BC+BS (each 1,000 kg ha−1). During the rice-growing season, significant interactive effects of BC and BS treatment were observed in major soil properties. The average rice yields in BC, BS, and BC+BS treatments increased by 4.6%, 4.7%, and 18.7%, compared with CN treatment, respectively. Also, BC+BS treatment produced relatively stable yield during the 3-year study. Both BC and BS applications, either alone or in combination, lowered soil bulk density values compared to the CN treatment. Further, BC application produced a low total CH4 flux than other treatments. The total produced GWP over the 3 years occurred in the order: BS ≧ CN > BC+BS > BC treatment. These results clearly demonstrate the advantages of biochar and straw applications in improving rice yield and soil fertility while reducing GWP and GHGI.

Microbial Community Abundance Affects the Methane Ebullition Flux in Dahejia Reservoir of the Yellow River in the Warm Season

Reservoirs are an integral part of the global carbon cycle and generally considered to be methane (CH4) emission hot spots. Although remarkable research achievements have been made concerning CH4 ebullition from inland waters, such as rivers, lakes, and ponds, few have been devoted to CH4 ebullition from plateau reservoirs. The present study focused on CH4 ebullition from the Dahejia Reservoir located in the upper reaches of the Yellow River. We analyzed the spatial and temporal characteristics of CH4 ebullition flux across the water-atmosphere interface between July and August 2021. We also evaluated the influence of microbes on CH4 ebullition flux. The results showed that (1) CH4 ebullition was the dominant mode of CH4 emissions in the study site, which contributed to 78.85 ± 20% of total CH4 flux. (2) The mean CH4 ebullition flux in the nighttime (0.34 ± 0.21 mg m−2 h−1) was significantly higher than that in the daytime (0.19 ± 0.21 mg m−2 h−1). The mean CH4 ebullition flux first decreased and then increased from the upstream (0.52 ± 0.57 mg m−2 h−1) to the downstream (0.43 ± 0.3 mg m−2 h−1) of the Yellow River. (3) Sediment microbes affected the CH4 ebullition flux primarily by changing the microbial community abundance. The regression analysis showed that CH4 ebullition flux had a significantly linear negative correlation with microbial abundance in sediments. The redundancy analysis further showed CH4 ebullition flux was significantly positively correlated with the abundances of Firmicutes and Actinobacteria, and negatively with that of Proteobacteria and Chloroflexi. Among abiotic variables, CH4 ebullition flux was closely related to total phosphorus, total organic carbon, pH and nitrate nitrogen.

Fine-Scale Assessment of Greenhouse Gases Fluxes from a Boreal Peatland Pond

Ponds are abundant in the boreal peatland landscape, which are potential hotspots for greenhouse gas (GHG) emissions. However, compared to large lakes, ponds are difficult to identify by satellite, and they have not been adequately studied. Here, we observed methane (CH4), carbon dioxide (CO2), and nitrous oxide (N2O) fluxes in the growing season at three sites along the water table gradient from the pelagic zone, littoral zone and bog across a shallow pond in a boreal peatland landscape in Northeastern China. The results showed that the littoral zone, dominated by herb Carex, was the hotspot for CH4 emissions. CH4 fluxes in littoral zone averaged 78.98 ± 19.00 mg m−2 h−1. The adjacent bog was a weak source of CH4 emissions, with an average flux of 0.07 ± 0.05 mg m−2 h−1. Within the pond, CH4 was mainly emitted through ebullition, accounting for 88.56% of the total CH4 fluxes, and the ebullition fluxes were negatively correlated with dissolved oxygen (DO). CO2 fluxes were highest in the pelagic zone, with an average of 419.76 ± 47.25 mg m−2 h−1. Wind and strong sediment respiration were key factors that led to the high fluxes. The observed three sites were all atmospheric N2O sinks ranging from −0.92 to −10.90 μg m−2 h−1. This study highlights the spatial variation in greenhouse gas fluxes from the pond and its adjacent bog, ignoring the ecotone area may underestimate CH4 fluxes. Although ponds are a hotspot for CH4 and CO2 emissions, they can also be a sink for N2O, which provides a reference for the quantification of global pond GHG fluxes. Therefore, finer-scale in situ observations are necessary to better understand the feedback of permafrost peatland ponds to global warming.

不同水生植物对景观水体CO2与CH4排放通量的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 不同水生植物对景观水体CO2与CH4排放通量的影响 DOI: 10.5846/stxb202206281837 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目(41807321);重庆市教委科学技术研究项目(KJZD-K202000502);大学生创新创业训练项目(202110637003) Effects of aquatic plants on the spatio-temporal variations of CO2 and CH4 fluxes in urban landscape waters Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:城市景观水体是大气CO2与CH4的排放热源,而水生植物作为景观水体的重要组成要素,对水体温室气体排放动态的影响并不清楚。选择重庆市观音塘国家湿地公园为研究区,利用漂浮箱法与顶空平衡法对观音塘水域7种不同水生植物分布区进行水-气界面CO2与CH4排放通量及CO2、CH4溶存浓度进行季节性监测,估算了植物传输对气体通量的贡献。结果表明:1)观音塘水体CO2与CH4浓度范围分别为8.0-341.8 μmol/L和0.23-5.26 μmol/L,排放通量分别为26.5-869.1 mmol m-2 d-1和0.40-11.15 mmol m-2 d-1,是大气净CO2与CH4排放源;2)观音塘开敞水区CO2与CH4排放通量低于大部分城市湖泊或景观水体,但植物覆盖区气体通量显著高于开敞水区,表明水生植物增强了景观水体温室气体排放;初步估算植物传输作用(非扩散通量)对水体CO2与CH4排放通量的贡献约为7.3%-44.6%与52.1%-63.4%,狐尾藻对CH4传输作用最强,睡莲、水葫芦次之,菖蒲、再力花、梭鱼草等挺水植物略低,苦草最弱,植物传输作用并未表现出明显的生活型差异;3)水体CO2与CH4浓度及排放通量季节变化显著,温暖季高于寒冷季,植物生长期变化与温度波动是主导水体CO2与CH4排放季节模式及变异强度的主要因素;4)水生植物覆盖区水体营养盐浓度、pH值、DO等因素与CO2、CH4排放通量呈显著的相关性,表明不同植物覆盖导致水生境的分异是影响水体CO2与CH4排放动态及变异性的重要机制。水生植物对水体温室气体产生、输移、排放等具有多重复杂机制,但总体增强了景观水体的温室气体通量,在未来城市水生态管理中应予以更多的关注。 Abstract:Urban landscape water is a hotspot of carbon dioxide (CO2) and (CH4) emissions to atmosphere, while little is known about the effect of aquatic plants, which is an important component of landscape water ecosystem, on greenhouse gas emissions dynamics in such water. In this study, we selected the Guanyin Pond National Wetland Park in Chongqing as a typical urban landscape water to carry out seasonal investigations for the fluxes and dissolved concentrations of CO2 and CH4 using floating chamber method and headspace method. The aims of this study were to explore contribution of aquatic plants to the spatio-temporal variations in aquatic CO2 and CH4 fluxes in urban landscape waters. The results showed that the concentrations of CO2 and CH4 ranged from 8.0-341.8 μmol/L to 0.23-5.26 μmol/L in Guanyin Pond, and the fluxes of CO2 and CH4 were ranging from 26.5 to 869.1 mmol m-2 d-1 and from 0.40 to 11.15 mmol m-2 d-1, respectively. Guanyin Pond was a net source of atmospheric CO2 and CH4. CO2 and CH4 fluxes in the open water area of Guanyin Pond were much lower than most of the reported values from ponds and lakes in urban area, while those in water area with aquatic vegetations distribution were much higher, indicating the aquatic plants enhanced the greenhouse gas emission of landscape water bodies. It was estimated that the plant transport contributed about 7.3%-44.6% and 52.1%-63.4% of total CO2 and CH4 fluxes from water-air surface, respectively. The contribution of plant transmission was different for different species despite no "biotype effect". The seasonal variations of CO2 and CH4 concentrations and fluxes in Guanyin Pond were significant with higher values in warm season and lower ones in cold season. We highlighted that the seasonal periodicity growth and temperature were main drivers for the seasonal patterns and variation intensity of CO2 and CH4 fluxes. Nutrients concentrations, pH and dissolved oxygen (DO) were influenced by aquatic vegetations distribution in Guanyin Pond, and were significantly correlated with CO2 and CH4 fluxes, indicating that the differentiation of water habitats caused by different aquatic plant species were important mechanism affecting the spatial variability of CO2 and CH4 dynamics. Despite mechanisms of aquatic plant impact on water CO2 and CH4 dynamics are complicated and various, aquatic plant distribution indeed enhance greenhouse gases fluxes of urban landscape water. Therefore, more attentions should be paid to the CO2 and CH4 dynamics in such special aquatic system in the future. 参考文献 相似文献 引证文献

Highest methane concentrations in an Arctic river linked to local terrestrial inputs

Abstract. Large amounts of methane (CH4) could be released as a result of the gradual or abrupt thawing of Arctic permafrost due to global warming. Once available, this potent greenhouse gas is emitted into the atmosphere or transported laterally into aquatic ecosystems via hydrologic connectivity at the surface or via groundwaters. While high northern latitudes contribute up to 5 % of total global CH4 emissions, the specific contribution of Arctic rivers and streams is largely unknown. We analyzed high-resolution continuous CH4 concentrations measured between 15 and 17 June 2019 (late freshet) in a ∼120 km transect of the Kolyma River in northeast Siberia. The average partial pressure of CH4 (pCH4) in tributaries (66.8–206.8 µatm) was 2–7 times higher than in the main river channel (28.3 µatm). In the main channel, CH4 was up to 1600 % supersaturated with respect to atmospheric equilibrium. Key sites along the riverbank and at tributary confluences accounted for 10 % of the navigated transect and had the highest pCH4 (41 ± 7 µatm) and CH4 emissions (0.03 ± 0.004 mmolm-2d-1) compared to other sites in the main channel, contributing between 14 % to 17 % of the total CH4 flux in the transect. These key sites were characterized by warm waters (T&gt;14.5 ∘C) and low specific conductivities (κ&lt;88 µS cm−1). The distribution of CH4 in the river could be linked statistically to T and κ of the water and to their proximity to the shore z, and these parameters served as predictors of CH4 concentrations in unsampled river areas. The abundance of CH4-consuming bacteria and CH4-producing archaea in the river was similar to those previously detected in nearby soils and was also strongly correlated to T and κ. These findings imply that the source of riverine CH4 is closely related with sites near land. The average total CH4 flux density in the river section was 0.02 ± 0.006 mmolm-2d-1, equivalent to an annual CH4 flux of 1.24×107 g CH4 yr−1 emitted during a 146 d open water season. Our study highlights the importance of high-resolution continuous CH4 measurements in Arctic rivers for identifying spatial and temporal variations, as well as providing a glimpse of the magnitude of riverine CH4 emissions in the Arctic and their potential relevance to regional CH4 budgets.

Strong methane point sources contribute a disproportionate fraction of total emissions across multiple basins in the United States

Understanding, prioritizing, and mitigating methane (CH4) emissions requires quantifying CH4 budgets from facility scales to regional scales with the ability to differentiate between source sectors. We deployed a tiered observing system for multiple basins in the United States (San Joaquin Valley, Uinta, Denver-Julesburg, Permian, Marcellus). We quantify strong point source emissions (>10 kg CH4 h-1) using airborne imaging spectrometers, attribute them to sectors, and assess their intermittency with multiple revisits. We compare these point source emissions to total basin CH4 fluxes derived from inversion of Sentinel-5p satellite CH4 observations. Across basins, point sources make up on average 40% of the regional flux. We sampled some basins several times across multiple months and years and find a distinct bimodal structure to emission timescales: the total point source budget is split nearly in half by short-lasting and long-lasting emission events. With the increasing airborne and satellite observing capabilities planned for the near future, tiered observing systems will more fully quantify and attribute CH4 emissions from facility to regional scales, which is needed to effectively and efficiently reduce methane emissions.

Global methane and nitrous oxide emissions from inland waters and estuaries.

Inland waters (rivers, reservoirs, lakes, ponds, streams) and estuaries are significant emitters of methane (CH4 ) and nitrous oxide (N2 O) to the atmosphere, while global estimates of these emissions have been hampered due to the lack of a worldwide comprehensive data set of CH4 and N2 O flux components. Here, we synthesize 2997 in-situ flux or concentration measurements of CH4 and N2 O from 277 peer-reviewed publications to estimate global CH4 and N2 O emissions from inland waters and estuaries. Inland waters including rivers, reservoirs, lakes, and streams together release 95.18 Tg CH4 year-1 (ebullition plus diffusion) and 1.48 Tg N2 O year-1 (diffusion) to the atmosphere, yielding an overall CO2 -equivalent emission total of 3.06 Pg CO2 year-1 . The estimate of CH4 and N2 O emissions represents roughly 60% of CO2 emissions (5.13 Pg CO2 year-1 ) from these four inland aquatic systems, among which lakes act as the largest emitter for both CH4 and N2 O. Ebullition showed as a dominant flux component of CH4 , contributing up to 62%-84% of total CH4 fluxes across all inland waters. Chamber-derived CH4 emission rates are significantly greater than those determined by diffusion model-based methods for commonly capturing of both diffusive and ebullitive fluxes. Water dissolved oxygen (DO) showed as a dominant factor among all variables to influence both CH4 (diffusive and ebullitive) and N2 O fluxes from inland waters. Our study reveals a major oversight in regional and global CH4 budgets from inland waters, caused by neglecting the dominant role of ebullition pathways in those emissions. The estimated indirect N2 O EF5 values suggest that a downward refinement is required in current IPCC default EF5 values for inland waters and estuaries. Our findings further indicate that a comprehensive understanding of the magnitude and patterns of CH4 and N2 O emissions from inland waters and estuaries is essential in defining the way of how these aquatic systems will shape our climate.

Methane emissions from forested closed landfill sites: Variations between tree species and landfill management practices

Trees in natural and managed environments can act as conduits for the transportation of methane (CH4) from below ground to the atmosphere, bypassing oxidation in aerobic surface soils. Tree stem emissions from landfill sites exhibit large temporal and spatial variability in temperate environments and can account for approximately 40% of the total surface CH4 flux. Emission variability was further investigated in this study by measuring CH4 and CO2 fluxes from landfill sites with different management strategies and varying tree species over a 7-month period. Stem and soil measurements were obtained using flux chambers and an off-axis integrated cavity output spectroscopy analyser. Analysis showed average stem and soil CH4 emissions varied significantly (p < 0.01) between landfills with different management practices. On average, tree stem CH4 fluxes from sites with no clay cap but gas extraction, clay cap and gas extraction, and no clay cap and no gas extraction were 1.4 ± 0.4 μg m−2 h−1, 47.2 ± 19.0 μg m−2 h−1, and 111.9 ± 165.1 μg m−2 h−1, respectively. There was no difference in stem CH4 fluxes between species at each site, suggesting environmental conditions (waterlogging) and site age had a greater influence on both stem and soil fluxes. These results highlight the importance of management practices, and the resultant environmental conditions, in determining CH4 emissions from historic landfill sites.

Rice husk and melaleuca biochar additions reduce soil CH 4 and N 2O emissions and increase soil organic matter and nutrient availability.

Background: Biochar is a promising material in mitigating greenhouse gases (GHGs) emissions from paddy fields due to its remarkable structural properties. Rice husk biochar (RhB) and melaleuca biochar (MB) are amendment materials that could be used to potentially reduce emissions in the Vietnamese Mekong Delta (VMD). However, their effects on CH 4 and N 2O emissions and soil under local water management and conventional rice cultivation have not been thoroughly investigated. Methods: We conducted a field experiment using biochar additions to the topsoil layer (0-20 cm). Five treatments comprising 0 t ha -1 (CT0); 5 t ha -1 (RhB5) and 10 t ha -1 (RhB10), and 5 t ha -1 (MB5) and 10 t ha -1 (MB10) were designed plot-by-plot (20 m 2) in triplicates. Results: The results showed that biochar application from 5 to 10 t ha -1 significantly decreased cumulative CH 4 (24.2 - 28.0%, RhB; 22.0 - 14.1%, MB) and N 2O (25.6 - 41.0%, RhB; 38.4 - 56.4%, MB) fluxes without a reduction in grain yield. Increasing the biochar application rate further did not decrease significantly total CH 4 and N 2O fluxes but was seen to significantly reduce the global warming potential (GWP) and yield-scale GWP in the RhB treatments. Biochar application improved soil Eh but had no effects on soil pH. Whereas CH 4 flux correlated negatively with soil Eh ( P < 0.001; r 2 = 0.552, RhB; P < 0.001; r 2 = 0.502, MB). The soil physicochemical properties of bulk density, porosity, organic matter, and anaerobically mineralized N were significantly improved in biochar-amended treatments, while available P also slightly increased. Conclusions: Biochar supplementation significantly reduced CH 4 and N 2O fluxes and improved soil mineralization and physiochemical properties toward beneficial for rice plant. The results suggest that the optimal combination of biochar-application rates and effective water-irrigation techniques for soil types in the MD should be further studied in future works.

Cover cropping and its biomass incorporation: Not enough to compensate the negative impact of plastic film mulching on global warming

Plastic film mulching (FM) became a general practice to enhance crop productivity and its net primary production (NPP), but it can increase greenhouse gas (GHG) emissions. The proper addition of organic amendments might effectively decrease the impact of FM on global warming. To evaluate the feasibility of biomass addition on decreasing this negative influence, cover crop biomass as a green manure was incorporated with different recycling levels (0–100% of aboveground biomass) under FM and no-mulching. The net global warming potential (GWP) which integrated with soil C stock change and GHG (N2O and CH4) fluxes with CO2-equivalent was evaluated during maize cultivation. Under the same biomass incorporation, FM significantly enhanced the grain productivity and NPP of maize by 22–61 and 18–58% over no-mulching, respectively. In contrast, FM also highly increased the respired C loss, which was 11–95% higher than NPP increase, over no-mulching. Irrespective with biomass recycling ratio and mulching system, negative NECB which indicates the decrease of soil C stock was observed, mainly due to big harvest removal. FM decreased more soil C stock by 57–158% over no-mulching, but its C stock was clearly increased with increasing biomass addition. FM significantly increased total N2O and CH4 fluxes by 4–61 and 140–600% over no-mulching, respectively. Soil C stock changes mainly decided net GWP scale, but N2O and CH4 fluxes negligibly influenced. As a result, FM highly increased net GWP over no-mulching, while this net GWP was clearly decreased with increasing biomass application. However, cover cropping, and its biomass recycling was not enough to compensate the negative impact of FM on global warming. Therefore, more biomass incorporation might be essential to compensate this negative effect of FM.

Controlling Factors of Seasonal Variation of Stem Methane Emissions From Alnus japonica in a Riparian Wetland of a Temperate Forest

AbstractTree‐mediated methane (CH4) emissions represent an uncertain pathway of the total CH4 flux released from forested ecosystems. We measured the stem CH4 fluxes from Alnus japonica in a riparian wetland of a temperate forest for a year from 2017 to 2018, using automated chambers. The stem CH4 fluxes varied seasonally, showing summertime maxima and wintertime minima. Medians of stem CH4 fluxes were 12.9, 0.5, 0.4, and 13.4 nmol m−2 s−1 during autumn, winter, spring, and summer, respectively. Dissolved CH4 concentration in groundwater beneath the trees was the major controlling factor of the stem CH4 fluxes. Temporal variations in soil environmental conditions (temperature and groundwater level) controlled dissolved CH4 concentrations in groundwater, and accordingly, stem CH4 fluxes. In addition, stem CH4 emissions were observed when the sap flux diminished during the defoliation period. These results indicate that CH4 in the rhizosphere is mainly transported in the gaseous form through intercellular space in trees. Intense rainfall occasionally caused a transient increase in the stem CH4 emissions, which was attributed to the temporal changes in the groundwater flow paths by rainfall affecting the belowground CH4 concentrations. Our findings highlight the need for continuous stem CH4 flux measurements for improved understanding of the controlling factors and future response of CH4 dynamics in forests, with regards to climate change.

Substantial Stem Methane Emissions From Rainforest and Cacao Agroforest Partly Negate Soil Uptake in the Congo Basin

AbstractMost stem CH4 emission investigations were conducted in wetland forests, and it remains unknown whether trees in tropical rainforests on heavily weathered soils are substantial contributors to ecosystem CH4 fluxes. Additionally, Africa remains the continent with the lowest numbers of published field studies on soil greenhouse gas fluxes. Over one year, we measured monthly stem and soil CH4 fluxes with forest conversion to traditional cacao agroforestry in the Congo Basin, Cameroon. All the measured trees emitted CH4 throughout the year. The annual total (soil + stem) CH4 fluxes were −2.62 ± 0.37 kg C ha−1 yr−1 from the forest and −3.23 ± 0.45 kg C ha−1 yr−1 for the cacao agroforestry, with stem CH4 emissions equating to 4%–21% of the soil sink in the forest, and 3%–27% of the soil sink in cacao agroforestry. 2% of our measured trees were “hot spots” of CH4 emission, with two orders of magnitude larger emissions than the remaining trees in our sites. Correlations of stem CH4 emissions and soil drivers suggest a potential belowground source of stem CH4 emissions, although this pathway may be working simultaneously with a within‐tree microbial CH4 source. Overall, forest conversion to traditional, mature cacao agroforestry did not affect stem and soil CH4 fluxes. Our results demonstrate that tropical trees on well‐drained, highly weathered soils represent potential CH4 emission pathways that have largely been ignored, and provides evidence that upland ecosystems may be weaker sinks of atmospheric CH4 than previously estimated.